Method of manufacturing prestressed concrete structural members



y 13, 1952 s.. MACERATA 2,596,495

METHOD OF MANUFACTURING PRESTRESSED CONCRETE STRUCTURAL MEMBERS Filed Dec. 31, 1947 Patented May 13, 1952 UNITED METHOD OF MANUFACTURING PRE- STRESSED CONCRETE STRUCTURAL MEMBERS Stelio Macerata, Johannesburg, Transvaal, Union of South Africa Application December 31, 1947, Serial No. 795,003. In Great Britain January 10, 1947 1 Claim. 1

This invention relates to the manufacture of structural members. More particularly, but not exclusively, this invention relates togirders, tension and compression members suitable for use in lattice girders, masts, and to columns.

A structural member according to this invention comprises a metal or other tube surrounding a core of cementitious material, which is reinforc'ed by pretensioned reinforcing wires or rods and is maintained in a state of compression within said tube even when said member is not exposed to any external load.

When the structural member is of substantial length, it may comprise a plurality of tubes, each two adjoining tube ends having interposed between them a member which provides an inlet for grout or mortar, and which is arranged to have passed therethrough the rods or wires. Such intermediate member may provide part of a strut or brace.

The invention also comprises a compound structure which comprises at least two structural members of the kind specified in either of the last two preceding paragraphs.

In accordance with the invention, a method of producing a structural member of the aforementioned type comprises the steps of providing a tube; closing the ends of the tube with closure members each of which is formed with a spigot which is seated in its respective tube end as in a socket; providing metal rods or wires extending axially through the whole length of said tube; anchoring the rods or wires to one of said closure members and allowing the opposite ends of said rods or wires to project through the other member; attaching said opposite ends of the rods or wires to a tensioning device which acts on the closure member through which the rod or wire ends project without being anchored thereto so as to tend to draw the closure members relatively towards one another when tension is applied to the rods or wires; filling the tube with an aggregate; tensioning the rods or wires by means of the tensioning device; forcing cementitious material into the tube under pressure to fill the interstices in the aggregate; and allowing the cementitious material to set. 7

If desired, the steps of tensioning the rods or wires and forcing cementitious material into the tube may be repeated alternately until the rods or wires are pretensioned to the required degree and the cementitious material and aggregate stressed to the required degree of compression.

To facilitate complete filling of the interstices with grout or mortar and to obtain a good distribution of pressure within the tube, vibration passed therethrough the rods or wires.

In a modification of the process of the invention, the rods or wires are from the start prestressed to the desired degree, and the tube (or the compound tube comprising at least two tubes and at least one member interposed between the adjacent ends of the two tubes) filled with aggregate, grout or cement mortar being thereafter forced in under pressure.

The invention will be further described with qreference to the accompanying drawings, in

which:

Figure 1 is a section of a structural member in the course of its manufacture.

Figure 2 is 'a section II--IIof Figure 1.

With reference to the figures, I and 2 indicate co-axially mounted tubular sections which may be made of metaLconcrete or other suitable material. Such tubular sections are sufiiciently strong to resist the radial pressure which will be imposed on them as hereinafter described. The end 3 of the section I is closed by a member 4 which provides a spigot 5 which is seated in the end 3 as in a socket. Similarly, the end 6 of the section 2 is closed by a member I providing a spigot 8 which is seated in the end 6.

Interposed between the respective ends 9 and I0 of the sections I and 2 is a member II] which provides an inlet conduit I2 through which cementitious material may be forced into the interior of the tubular sections I and 2. Rubber gaskets I3 which are held in place by clamps I4 are used to insure a tight connection between the sections I and 2 and the members 4, I and I I.

I5 are reinforcing rods or wires which are anchored in the members I as by a cross-piece I5 and the free ends I! of such rods or wires project through holes I8 in the member 4. Said free ends ll further pass through a clamp I9 which is seated on the member 4, and are connected to a suitable tensioning device, e. g. to one of the movable parts of a hydraulic jack (not shown), the other movable part of which is arranged to rest on and to act upon the clamp I9. The rods or wires I5 also pass through holes ZI in the member II. The size of the holes I B and 2| relative to that of the rods or wires 2,596,495 7 f, V a

I5 is such that when tension is applied to the rods or wires, they are just free to move relative to the members I and II.

In accordance with the method of the invention, the tubular sections I and 2 are first of all filled with aggregate. This may conveniently be done when the sections are being assembled to the members 4, I and II. The rods or wires I5 are slightly tensioned and thereafter grout or cement mortar is forced into the sections through the inlet conduit I2, until they are completely filled (as may be shown by a tendency for the grout or mortar to be pressed out of the sections at the joints of the latter with the members 4 and l). Thereupon, tension ofthe rods or wires is increased and additional groutor mortar is forced into the tubular sections, and the steps of increasing the tension of the rods or wires and of forcing additional grout or mortar into the sections are repeated until the rods or wires are tensioned to the required degree of pre' stressing and the core stressed tothe required degree ofcompression. The oernentitious material is then allowed to set. 7

When grout or cement mortar is, as aforementioned, -forced into the tubular sections, the pressure" will tend to move the end closure members 4 and I outwards relative to the sections after the free space or the latter has been completely filled, and at least traces of the grout or mortar willaccordingly show at the ends 3 andB-of the respective sections I and 2. When, thereafter, the tension on the rods or wires I 5 is further increased by, pulling directly on them '(the grout or mortar inlet I2 being blocked against return flow), the increased tension and reaction on the closure members '4 and 'I will tend to force the latter to return to their original positions." At the same time the pressure of the coreisincreased.

The repetition of the steps of tensioning the rods or wires and forcing grout or mortar into the sections is necessary order to settle the material down and produceahomogeneous compacted core. From a practical point of view, satisfactory compactionoflthe core is not otherwise achieved.

Aiter the cementitious material has. set; the tensioning means removed. With relatively longmulti-section structures, the. clamps may also beremoved; but ifthe structures are short, they are preferably left in place. The projecting ends of the rodsor wires I5 are out 01f, if desired, and the structural member is ready for use.

Due to the -pre-stressing of the cementitious core, the tube I; is normally tensioned and if an axial directload is applied to a structural member of the a foresaid kind, the said core becomes further compressed and, as a result, the tension in the tube I tends to increase.

Suchlateral restraint brings about an increase inbondbetween the material of said cementitious 4 core 23 and the reinforcing rods or wires I5 embedded therein and at the same time an increase in the ultimate compressive strength of the cementitious core and, accordingly, of the structural member of this invention.

I claim:

A method of forming'an extended structural member originally consisting of a plurality of tubular sections and each respectively provided with a filling conduit, and having end closures with a plurality of tensioning rods extending longitudinally through the inside hollow passages of the tubular "sections and through theend c10- sures so that said rods may be accessible for tensioning by means external of the structural member, to tightly press the end closures against the structural member, said method consisting of' filling the tubular sections with aggregate while they are being assembled end to end; connecting and sealing juxtaposed ends of the respective adjacent sections to permit free passage of cementitiou'smaterial and to sealthose ends tolimit leakage of the cementitious material; similarly closing and sealing the outerends of the-extended member at the end closures to limit leakage; tensioning the several rodsj forcingcementitious material under compression into the tubular secs tions through the conduits until the compression of the filling material exhibits oozing rat the sealed regions; re-tensioning the several tension rods to further compress the fiiling'material'g ad-v ,ditionally packing more 'cementitious, material into the structural member until oozing is again manifested; and repeating "such further. tension-- ing'of the tension rods and pressure. filling of the structural member with cementitious material until the compression value of thefilling material attains a predetermined value; and then allowing the cementitious material toset.

STELIO r/moansm.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES-PATENTS 

